The present invention is with respect to a method and a circuit system for the automatic switching over from the playback of an announcement text to storing a message from a caller in an automatic telephone answering apparatus having an announcement unit with an announcement tape and a message recording unit with a message recording tape for incoming messages.
A circuit system on these lines has been put forward in the prior art, see German Auslegeschrift specification No. 2,205,919. In this known circuit a switch over signal is produced, it being recorded after the announcement text on the announcement tape and having to be different to the speech signals. On the receipt of an incoming call, the announcement tape is played back and the switch over signal made out with a specially designed detector circuit. Dependent on triggering of the detector circuit by the switch over signal, there is then an automatic switch over from the playback of the announcement text to recording of the incoming message. In this known circuit, the system in it for producing a switch over signal and for making out the switch over signal on playback is undesirably complex, a signal generator for producing a certain switch over signal and a filter for use in detecting the switch over signal on playback being necessary. What is more, it is important that the tape be transported at the same, unchanging speed on recording and playback of the switch over signal, because the frequency is important for detecting the switch over signal.
For this reason, one may not be certain of being able to make out the switch over signal or, if certain detection is desired, the filters, for example, have to be within a tight tolerance range.